It is a well known and well documented fact that the demand for blood supplies for administration to patients undergoing surgery and other emergency medical procedures has increased very rapidly over the past 30 years or so. The demand often exceeds the supplies available from human donors. Even larger volumes of blood would be used if it were readily available. Elective surgery is often postponed because of shortages of blood. Medical techniques continue to become more sophisticated and successful, so that the amounts of blood required continue to increase. Extracorporeal techniques require large quantities of blood, mostly for temporary use. There is therefore a need to develop blood substitutes, and to make the most efficient use of blood supplies which are available. This need exists not only in areas where advanced medical techniques are practiced, but also in underdeveloped areas of the world where expensive facilities for blood banking and blood typing are not available.